Here is some advice (I'm following a walkthrough here, and this sounds where you might be in the game).
At the top, look down from the center of the rings to see a large lever. Click on it to hear Umang say "It needs something else." Climb down the stairs. Go right around to the front of the rings again and climb up that last set of stairs. "Hmm....some kind of strange mechanism," says Umang, as he faces a huge black button on the base of the support holding the rings aloft. Click on the button to reveal that it is likely the receptacle for the tetrahedron you've been lugging around for a long time. But first let's get those four control panels on the four surrounding pedestals set properly according to the graphic in your journal.
Let us know if you need more help.